Goodman Gallery security guard Paul Molesiwa has been acquitted of assaulting one of the men who defaced a controversial painting of President Jacob Zuma, The Citizen reported on Monday.

Molesiwa's attorney Cliff Alexander said the State could not prove his client had acted with intent to commit grievous bodily harm when he arrested Louis Mabokela on May 22, 2012.

"The court found he didn't exceed the bounds of self-defence and he did not exceed the bounds of section 49 of the Criminal Procedure Act."

Mabokela was last year convicted of malicious damage to property for smearing black paint on the portrait "The Spear", which depicted Zuma with his genitals exposed. He received a six month jail sentence, suspended for five years.

Professor Barend la Grange of Wits University paid a R1000 fine for his protest in the gallery, which saw him painting red crosses over the Brett Murray painting on the same day.